Berkshire Limestone. 297 



of peroxide and 31 of protoxide, could have been produced in con- 

 junction with the limestone. 



The encrinal remains in the Bernardston limestone are usually 

 quite imperfect ; but the transverse septa and the central perforation 

 are generally distinct. Plate XIV. fig. 47, exhibits an end view of 

 one encrinus, about an inch in diameter ; and a view of another, lying 

 horizontally in the rock. 



Berkshire Limestone. 



This rock constitutes a portion of that extensive calcareous forma- 

 tion, which occupies the western part of. Connecticut, Massachusetts, 

 and Vermont. It is one of the most extensive ranges of limestone 

 in the world, if we regard it as primary, according to the general 

 opinion of writers. That a part of it is primitive, in the Wernerian 

 acceptation of the term, there can be no doubt : for it is interstratified 

 with gneiss and mica slate in the eastern part of the range, and it is 

 highly crystalline in its texture. But as we go westerly, the inter- 

 stratified mica slate passes into clay slate, and the limestone becomes 

 less crystalline, and assumes a gray, and finally a dark color. Pass- 

 ing still farther west, across the clay slate, into New York, we soon 

 come to a range of limestone decidedly more recent, which Professor 

 Dewey has denominated transition limestone, and Professor Eaton, 

 metalliferous limestone. Crossing this rock, which is only a few 

 miles wide, we reach decided graywacke ; and this, with some inter- 

 ruptions of limestone, continues nearly to Hudson river ; as may be 

 seen on the Geological Map by Prof. Dewey, in the 8th vol. of the 

 American Journal of Science, and on the Geological Section of Prof. 

 Eaton in his " Canal Rocks." 



From this statement the geologist infers at once, that here is a 

 gradual passage from the oldest limestone to that which is associated 

 with graywacke. But a singular anomaly in the superposition of the 

 series of rocks above described, presents a great difficulty in this case. 

 The strata of these rocks almost uniformly dip to the east : that is, 

 the newer rocks seem to crop out beneath the older ones ; so that the 

 saccharine limestone, associated with gneiss in the eastern part of 

 the range, seems to occupy the uppermost place in the series. Now 

 as superposition is of more value in determining the relative ages of 

 rocks than their mineral characters, must we not conclude that the 

 rocks, as we go westerly from Hoosac mountain, do in fact belong to 

 older groups ? The petrifactions which some of them contain, and 

 38. 



